In vitro evaluation of an easy-to-remove orthodontic adhesive with photochromic property

OBJECTIVES

To develop a photochromic bracket adhesive (PCA) with modification using photochromic material and evaluate the biocompatibility, bond strength, photochromic property, and adhesive removal efficiency.

MATERIALS AND METHODS

The resin-modified glass ionomer powder was mixed with the photochromic material and then blended with the liquid agent to form PCA. Biocompatibility was evaluated by CCK-8 kit, and shear bond strength (SBS) was measured. Stereoscopic microscopy and quantitative color analysis were used to assess the photochromic property. Bracket bonding and debonding procedures were performed on a head simulator with the assistance of an ultraviolet radiator. The effectiveness of adhesive removal during bonding and debonding procedures was assessed using a stereomicroscope. Removal time was recorded, and the enamel damage index after debonding was analyzed.

RESULTS

CCK-8 assay and SBS test indicated that 5wt.% mixing ratios of the photochromic material did not compromise the biocompatibility and SBS of the adhesive (PCA5). PCA5 showed photochromic properties and could help the operator remove adhesive more thoroughly without increasing enamel damage.

CONCLUSIONS

Photochromic adhesive (PCA5) can be good for orthodontic adhesive removal and therefore has good clinical translation potential.

Intramolecular excimers of open forms of 2H-benzopyran, 2H- and 3H-naphthopyrans in solution: TD-DFT/DFT analysis

We hypothesized that in the open forms of diphenyl-substituted photochromic compounds, immediately after the photoinduced cleavage of the C-O bond, one of the phenyl rings forms a stack with an aromatic system at the other end of the alkyl linker. The formation of these intramolecular stacking excimers is made possible by a known increase in the rotational mobility of the linker double bonds in the excited state. The flexibilities of linkers are analyzed in terms of changes in their dihedral angles. After internal conversion, stacking is partially broken but it still prevents the recovery of the C-O bond. This explains the significantly greater stability of the open forms of diphenyl-substituted benzopyran and naphthopyran compared to dimethyl-substituted ones. Open structures with residual stacking are intermediate and by thermal motion, they transform into stable trans-trans and cis-trans forms. However, in our opinion, they significantly affect the equilibrium of closed and open isomers in solution. In particular, the calculated stacking energy of 2H-naphthopyran turned out to be higher than that of 3H-naphthopyran, which partly explains the significantly greater stability of the open form of the former. For the DFT/TD-DFT calculations performed in this work, the following functionals were selected to provide reliable stacking for the open forms of all three studied compounds: APFD, M052X, M06HF, as well as B3LYP with D3(BJ) Grimme dispersion correction. The 6-311++G(d,p) basis set and cyclohexane solvent modeled using IEFPCM were also used.

Photoswitchable Photochromic Chelating Spironaphthoxazines: Synthesis, Photophysical Properties, Quantum-Chemical Calculations, and Complexation Ability

The stable and efficient photochromic and photoswitchable molecular systems designed from spirooxazines are of increasing scientific and practical interest because of their present and future applications in advanced technologies. Among these compounds, chelating spironaphthoxazines have received widespread attention due to their efficient optical response after complexation with some metal ions being of biomedical interest and environmental importance, as well as their good cycle performance and high reliability, especially by metal ion sensing. In this mini-review, we summarize our results in the design of novel photoswitchable chelating spironaphthoxazines with specific substituents in their naphthoxazine or indoline ring systems in view of recent progress in the development of such molecular systems and their applications as metal ion sensors. The design, synthesis methods, and photoresponse of such spirooxazine derivatives relevant to their applications, as well as quantum-chemical calculations for these compounds, are presented. Examples of various design concepts are discussed, such as sulfobutyl, hydroxyl, benzothiazolyl, or ester and carboxylic acid as substituents in the chelating spironaphthoxazine molecules. Further developments and improvements of this interesting and promising kind of molecular photoswitches are outlined.

Naphthopyran molecular switches and their emergent mechanochemical reactivity

Naphthopyran molecular switches undergo a ring-opening reaction upon external stimulation to generate intensely colored merocyanine dyes. Their unique modularity and synthetic accessibility afford exceptional control over their properties and stimuli-responsive behavior. Commercial applications of naphthopyrans as photoswitches in photochromic ophthalmic lenses have spurred an extensive body of work exploring naphthopyran-merocyanine structure-property relationships. The recently discovered mechanochromic behavior of naphthopyrans has led to their emergent application in the field of polymer mechanochemistry, enabling advances in the design of force-responsive materials as well as fundamental insights into mechanochemical reactivity. The structure-property relationships established in the photochemical literature serve as a convenient blueprint for the design of naphthopyran molecular force probes with precisely tuned properties. On the other hand, the mechanochemical reactivity of naphthopyran diverges in many cases from the conventional photochemical pathways, resulting in unexpected properties and opportunities for deeper understanding and innovation in polymer mechanochemistry. Here, we highlight the features of the naphthopyran scaffold that render it a powerful platform for the design of mechanochromic materials and review recent advances in naphthopyran mechanochemistry.

New Luminescent Pyridine-based Disc type Molecules: Synthesis, Photophysical, Electrochemical, and DFT studies

The design and synthesis of new conjugated luminescent molecules have attracted the attention of researchers because of their various applications, especially in the field of optoelectronic devices. Most of the applications were mainly based on the intramolecular charge transfer (ICT). For this purpose, we designed and synthesized a series of new donor-acceptor based disc type molecules i.e. 2,4,6-tris(4-(alkyloxy)phenyl)pyridines carrying variable alkoxy chains [i.e. n = 2, 4, 6, 8, 10, 12, 14, 16]. Further, the structures of all the synthesized compounds were confirmed by using ATR-IR, ¹H-NMR, ¹³C-NMR, and ESI-MS analysis. Moreover, the photophysical property study indicated that all the molecules are blue light emitting materials, however the change of alkoxy chain length in phenyl arms does not affect their absorption, emission, and energy levels. Besides, the thermal study revealed that core is stable up to 350 °C. Also, the DFT study showed that the photo induced electron transfer caused by HOMO-LUMO excitation in the studied molecules. Therefore, all the molecules have potential applications in optoelectronic applications.

Blockade of persistent colored isomer formation in photochromic 3H-naphthopyrans by excited-state intramolecular proton transfer

In photochemistry the excited-state intramolecular proton transfer process (ESIPT) is often observed as a highly efficient singlet excited state depletion pathway, which in the presence of a strong intramolecular hydrogen bond may proceed on a subpicosecond time scale. The present work describes the suppression of unwanted transoid-trans isomer formation in photochromic 3H-naphthopyran derivatives by the introduction of a 5-hydroxy substituent. According to time-resolved spectroscopy experiments and excited-state ab initio calculations, transoid-cis → transoid-trans photoisomerization is reduced by a competitive ESIPT channel in nonpolar solvent (cyclohexane). Upon specific solute–solvent interactions (methanol, acetonitrile) the intramolecular hydrogen bond in the transoid-cis form is perturbed, favoring the internal conversion S1 → S0 process as photostabilizing channel.

Mechanistic insights into photochromic 3H-naphthopyran showing strong photocoloration

3,3-Diphenylbenzo[f]chromene (1) represents an important architectural platform for photochromic systems. Since the practical utility of such chromophores is largely dependent upon the kinetics of coloration and decoloration, elucidating the mechanistic details of these processes is of great value. Toward this end, we studied the photochromic reaction of (3-(2-methoxyphenyl)-3-phenyl-3H-benzo[f]chromene (2) by both time-resolved UV–vis and mid-IR spectroscopies. We found that irradiation of 2 at 365 nm generates long-lived colored transoid-cis isomers with lifetimes of 17.1 s and 17.5 min (at 21 °C) and even longer-lived transoid-trans isomers with a lifetime of 16 h. These experimental results were supplemented with ab initio ground-state and excited-state calculations, and the resulting theoretical interpretation may be useful for the design of new photochromic systems with optimized photofunctionality.

Facile Synthesis of 2H-Benzo[h]Chromenes via an Arylamine-Catalyzed Mannich Cyclization Cascade Reaction

A simple arylamine-catalyzed Mannich-cyclization cascade reaction was developed for facile synthesis of substituted 2H-benzo[h]chromenes. The notable feature of the process included the efficient generation of ortho-quinone methides (o-QMs) catalyzed by a simple aniline. The mild reaction conditions allowed for a broad spectrum of 1- and 2-naphthols and trans-cinnamaldehydes to engage in the cascade sequence with high efficiency.

Control of the Photo-Isomerization Mechanism in 3H-Naphthopyrans to Prevent Formation of Unwanted Long-Lived Photoproducts

In the photochromic reactions of 3H-naphthopyrans, two colored isomers TC (transoid-cis) and TT (transoid-trans) are formed. In terms of optimized photo-switchable materials, synthetic efforts are nowadays evolving toward developing 3H-naphthopyran derivatives that would not be able to photoproduce the long-living transoid-trans, TT, photoproduct. The substitution with a methoxy group at position 10 results in significant reduction of the TT isomer formation yield. The TC photophysics responsible for TT suppression were revealed here using a combination of multi-scale time resolved absorption UV-vis spectroscopy and ab initio calculations. The substitution changes the TC excited-state potential energy landscape, the bicycle-pedal isomerization path is favored over the rotation around a single double bond. The bicycle-pedal path is aborted in halfway to TT formation due to S₁→S₀ internal conversion populating back the TC species in the ground electronic state. This is validated by a shorter TC S₁ state lifetime for methoxy derivative in comparison to that of the parent-unsubstituted compound (0.47 ± 0.05 ps vs. 0.87 ± 0.09 ps) in cyclohexane.

Historical Development, Applications and Advances in Materials Used in Spectacle Lenses and Contact Lenses

Lenses used in vision correction have evolved from the initial glass reading stone of the 10th century to the currently anticipated planar metalens made from "nanopillars" of titanium dioxide. With ideas from early scientific minds being translated into reality, and military commissioned concepts adapted for civilian use, spectacle lens and contact lens materials have progressed significantly over the last century, with the expectation of further lens material innovations ahead. The purpose of this article is a review of literature on the historical developments and advances in spectacle lens and contact lens materials.

Spirooxazine dyes

This article provides an introductory overview of a class of colorant that underpinned the establishment of the most industrially important application of photochromic dyes. It outlines the properties that led to the rise (and subsequent decline) in commercial significance of spirooxazine colorants, and which attract researchers seeking to put them to work in new technologies. Within this survey, the chief means of synthesising such dyes and adjusting their photochromism are briefly discussed. The reader is directed to useful sources of information concerning not only these aspects, but also potential applications for spirooxazine-based photochromism.

Naphthopyran Dyes

This article covers the most commercially important type of photochromic dye. It outlines which of its subclasses are of most use and how they are manufactured. The history of the industrial exploitation of this kind of colorant is briefly given before illustrating its versatility with examples of the most useful ways in which photochromic properties can be manipulated by making adjustments to molecular structure.

Photochromic reaction in 3H-naphthopyrans studied by vibrational spectroscopy and quantum chemical calculations

Structural details on the species involved in the photochromic reaction of 3H-naphthopyrans in solution have been formerly determined using NMR spectroscopy. Herein we show that at room temperature time-resolved FT-IR spectroscopy is a simple and efficient tool for structural characterization of colored species generated upon continuous UV light irradiation of the model compound 3H-naphthopyran: 3,3-diphenyl-3H-naphtho[2,1-b]pyran. In solution and in the polymer matrix phase, a colored species transoid-cis is formed after a single-photon excitation process, while transoid-trans is a secondary long-lived photoproduct generated after two-step excitation involving two photons. Understanding the reaction mechanism leading to long-lived colored species can help with the design of new 3H-naphthopyran derivatives structurally optimized for making a photochromic reaction free from transoid-trans products, which is often important for applications. Ab initio calculations show that photoinduced ring-opening followed by isomerization occurs on a multidimensional potential-energy surface. The barriers separating the considered isomeric forms, both in the ground and in the excited state, help to interpret the step-by-step dynamics of the photoprocesses. The system is composed of a variety of ground state equilibrium forms. Each of them is characterized by fast excited-state deactivation pathways which may drive the system through different conical intersection regions.

Photochemistry of Photochromic Benzopyrans Studied by Time-Resolved Absorption Spectroscopy

Photochromic reactions of 2H-benzopyrans have been extensively studied to design new materials for commercial applications such as optical memories. Photochromism of 2H-benzopyrans proceeds from a C–O bond cleavage of the colorless closed form to give the colored open forms, which can thermally revert back to the original closed form. From time-resolved absorption spectroscopy, the ring opening of 2H-benzopyrans, 2,4-diphenyl-and 2,2,4-triphenyl-2H-benzopyran, is found to occur via the excited singlet state within 2 ps to produce vibrationally excited open forms in the ground electronic state. In the subnanosecond to submillisecond time domain, several decay components are observed. These components are assigned to respective stereoisomers with respect to two double bonds and one single bond of the open enone forms. As revealed from pump-laser power dependencies of the yields of the open forms, the photocleavage of the benzopyran molecules gives at first only the open forms revertible to the closed form by a single-bond rotation, and the photoexcitation of the first generated open forms gives rise to other open forms that need a double-bond rotation for reversion to the original closed form. Such a two-step two-photon photochromism can be expected to have a wide range of application.

Photochromic Materials by Postpolymerisation Surface Modification

Photochromic materials are available by a postpolymerization surface modification of diverse polymers in a multistep sequential process mediated, first, by carbene insertion chemistry, second, by diazonium coupling with a tethered precursor, and finally by coupling to a spiropyran. This three-step sequence is efficient, and surface loading densities of 10¹³ molecules cm^-2 are typically achievable, leading to materials with observable photochromic and wettability behavior, which operate over multiple cycles without significant photobleaching or loss of efficacy. Materials suitable for application in this process include both reactive, but also lower surface energy polymers. Although the process is particularly efficient for high surface area materials, surface modification onto lower surface area substrates, while being intrinsically less efficient, is nonetheless sufficiently effective that changes in macroscopic photochromic properties are readily observable.

Photochromic Polyurethanes Showing a Strong Change of Transparency and Refractive Index

Photochromic polymers have been studied as rewritable systems for optical elements with tunable transparency in the visible and refractive index in the NIR. Six diarylethene monomers have been synthesized to give thin films of photochromic polyurethanes. The absorption properties of the monomers in solution and of the corresponding polymeric films have been evaluated showing that a transparency contrast in the visible spectrum of the order of 103 can be obtained by a suitable choice of the chemical structure and illumination wavelength. The change in the refractive index in the NIR have been determined by ellipsometry showing changes larger than 10−2. A trend of this variation with the absorption properties has been also highlighted. Fresnel lenses working on the basis of both a change of the transparency and the refractive index (amplitude and phase) have been demonstrated.

Phototropic Guest-Host Liquid Crystal Systems: Environmental Effects on Naphthopyran Kinetics

Photoinduced isothermal and order-increasing phase transitions can be observed in guest-host liquid crystal mixtures containing naphthopyran derivatives. The changes are attributed to the different geometry and a less energetically favorable interaction with the liquid crystal molecules for the ground state naphthopyran species with respect to the photoproduct. In this study, we have investigated the thermal relaxation of the naphthopyran photoproduct back to the initial species as a function of temperature and excitation conditions. It was found that the thermal relaxation is typically first-order and its characteristic rate has a temperature dependence that is different in the anisotropic and isotropic states of the mesogenic solvents. In particular, the activation energy for thermal relaxation is larger in the ordered phases of mesogenic solvents relative to their isotropic phase. The findings suggests that the naphthopyran relaxation is hindered by the organization of the host environment. These results will be useful to build a more complete understanding of the mutual guest-host interactions in naphthopyran-containing guest-host LC systems.

Quantification of photoinduced order increase in liquid crystals with naphthopyran guests

Photoinduced order-increasing phase transitions can occur in dye-liquid crystal mixtures when the photoproduct of the excitation of the dye molecules is more compatible with the liquid crystalline medium than the initial dye species. A detailed investigation of the photoinduced changes of the phase behavior and optical properties of mixtures of liquid crystals with naphthopyran guests upon exposure to light at 365 nm is presented here. In these guest-host systems, the nematic-to-isotropic phase transition temperature is increased upon irradiation. We show that the nematic range can be extended up to 2.9 °C by illumination in 5CB (4-n-pentyl-4'-cyanobiphenyl) liquid crystal mixtures. The order parameter is significantly increased by illumination at all temperatures within the nematic range and the changes are larger at higher concentrations of the guests. In particular, the illuminated guest-host mixtures exhibit order parameters close to those of the neat liquid crystal host at the same temperature relative to the clearing point. An improved understanding of the photophysical processes taking place at the molecular level in these material systems can inform the design of photoresponsive materials and enhance their potential utility in optical or photonic devices.

Photoresponsive and wetting performances of sheet-like nanostructures of tungsten trioxide thin films grown on wood surfaces

Tungsten trioxide films with sheet-like nanostructures coated on wood substrates possessed photoresponsive behavior and superhydrophobic performance after OTS treatment.

Characterization of a photochromic intraocular lens

We demonstrate an optical setup for characterization of a photochromic intraocular lens and present first measurement results of the kinetic properties and relative spectral transmittance of this photochromic lens. The lens showed a main absorption spectrum with a center wavelength of λ(c)=405 nm and a minimum relative transmission of 74% in the activated state. The coloring and bleaching times were within the manufacturer-provided specification of approximately 10 s for coloring and 30 s for bleaching.

Performances of volume phase holographic grating for space applications: study of the radiation effect

The special properties of volume phase holographic gratings make them promising candidates for spectrometry applications where high spectral resolution, low levels of straylight, and low polarization sensitivity are required. Therefore it is of interest to assess the maturity and suitability of volume phase holographic gratings as enabling technologies for future space missions, with demanding requirements for spectrometry. One of the main areas of research is related to grating ageing under space radiation. In the present paper, two volume grating technologies are analyzed and compared under gamma irradiation. The performances of both technologies, the photo-thermo-refractive glass and the Dichromated Gelatin, are tested on samples and assessed in the Hα and near-infrared bands. The diffraction efficiency degradation under gamma irradiation is assessed.

Physicochemical study of spiropyran-terthiophene derivatives: photochemistry and thermodynamics

The photochemistry and thermodynamics of two terthiophene (TTh) derivatives bearing benzospiropyran (BSP) moieties, 1-(3,3″-dimethylindoline-6'-nitrobenzospiropyranyl)-2-ethyl 4,4″-didecyloxy-2,2':5',2″-terthiophene-3'-acetate (BSP-2) and 1-(3,3″-dimethylindoline-6'-nitrobenzospiropyranyl)-2-ethyl 4,4″-didecyloxy-2,2':5',2″-terthiophene-3'-carboxylate (BSP-3), differing only by a single methylene spacer unit, have been studied. The kinetics of photogeneration of the equivalent merocyanine (MC) isomers (MC-2 and MC-3, respectively), the isomerisation properties of MC-2 and MC-3, and the thermodynamic parameters have been studied in acetonitrile, and compared to the parent, non-TTh-functionalised, benzospiropyran derivative, BSP-1. Despite the close structural similarity of BSP-2 and BSP-3, their physicochemical properties were found to differ significantly; examples include activation energies (E(a(MC-2)) = 75.05 kJ mol(-1), E(a(MC-3)) = 100.39 kJ mol(-1)) and entropies of activation (ΔS = 43.38 J K(-1) mol(-1), ΔS = 37.78 J K(-1) mol(-1)) for the thermal relaxation from MC to BSP, with the MC-3 value much closer to the unmodified MC-1 value (46.48 J K(-1) mol(-1)) for this latter quantity. The thermal relaxation kinetics and solvatochromic behaviour of the derivatives in a range of solvents of differing polarity (ethanol, dichloromethane, acetone, toluene and diethyl ether) are also presented. Differences in the estimated values of these thermodynamic and kinetic parameters are discussed with reference to the molecular structure of the derivatives.